Efficacy of pulse oximetry and capnometry in postoperative ventilatory weaning

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Abstract
We examined the ability of capnometry and pulse oximetry to identify potential respiratory problems by comparing oxyhemoglobin saturation (O2Sat) as measured by pulse oximetry and end-tidal CO2 (PetCO2) with arterial blood gas (ABG) determinations in 40 mechanically ventilated ICU patients. Hemoglobin saturation as measured by pulse oximetry correlated significantly with PaO2 (r = .65, p less than .0001); more importantly, an oximeter O2 Sat less than 95% showed 100% sensitivity in identifying hypoxemia (i.e., PaO2 less than 70 torr). PetCO2 tended to correlate strongly with PaCO2 for individual patients, but not when evaluated as a screening tool for identifying ventilatory abnormalities in the overall group (r = .52, p less than .0001). A PetCO2 less than 26 torr identified hypocarbia (defined as PaCO2 less than 30 torr) with a sensitivity of 85%. However, a PetCO2 of greater than 40 torr predicted hypercarbia (PaCO2 greater than 45 torr) with a sensitivity of only 28%. The efficacy of pulse oximetry and capnometry in monitoring respiratory status during postoperative ventilatory weaning was examined in a subset of 24 patients who had undergone elective cardiac surgery. All patients were weaned by intermittent mandatory ventilation, but each was assigned randomly to either a control group monitored with periodic ABG sampling or to an experimental group, monitored by following PetCO2 and O2 Sat via pulse oximetry. In the experimental group, ABG values were obtained on ICU admission, but thereafter only if a) O2 Sat less than 95%, b) PetCO2 less than 26 or greater than 40 torr, or c) felt to be clinically indicated by ICU staff.(ABSTRACT TRUNCATED AT 250 WORDS)

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